1. Field of the Invention
The present invention relates to magnetic recording and reproduction apparatuses and methods therefor, and more particularly, to a magnetic recording and reproduction apparatus and a method therefor, in which digital data is recorded by a helical scanning method or reproduced.
2. Description of the Related Art
Portable digital video tape recorders including cameras (digital camcorders) and installation-type digital video tape recorders have been available these days, which are recording and reproduction apparatuses for recording digital video signals and digital audio signals into magnetic tape.
As a recording method for the above digital video tape recorders, a so-called DV method (IEC 61834 Helical scan digital video tape cassette recording system using 6.35 mm magnetic tape for consumersxe2x80x94525/60, 625/50, 1125/60, and 1250/50 systems) is used. The assignee of the present invention has filed two related applications (U.S. Pat. No. 5,926,604 and U.S. Pat. No. 6,028,726).
In the DV method, video tape 6.35 mm (=xc2xc inches) wide is used, which is narrower than video tape used in related analog video tape recorders by their recording methods, such as an 8-mm method (IEC 60843 Helical scan video tape cassette recording system using 8 mm magnetic tape for consumers).
In the DV method, although the tape width is smaller than that conventionally used, since a signal to be recorded is compressed and a recording density is increased, the DV method allows higher-quality recording for a longer period than recording methods for related analog video tape recorders.
FIG. 4 shows a track structure in the DV method. From the top of a track, an insert-and-track-information (ITI) sector serving as a time-axis reference during so-called after recording, an interference area (ITG: inter-track gap) (GAP), an audio (Audio) sector, another interference area (GAP), a video (Video) sector, yet another interference area (GAP), and a sub-code (Sub-code) sector are sequentially disposed.
In the DV method, one frame of a video signal conforming to the NTSC system is recorded into each of a total of 10 (12 for PAL) tracks. This means that a track has a constant relationship with a frame.
Therefore, when a desired video (frame) is searched for by fast forwarding magnetic tape while video is viewed, namely, during a variable-speed reproduction using a so-called search function, for example, since a track has a constant relationship with a frame, even if reproduction starts at any position in magnetic tape, video can be displayed after data is read from a predetermined number of tracks, and it is very easy to identify the position of the desired frame in the magnetic tape.
In a method for recording digital data which includes a video signal and an audio signal compressed by the MPEG-2 method, for example, since a track does not have a constant relationship with a frame due to the characteristics of the compression process, it is difficult to identify the position of a desired frame in magnetic tape. In addition, when reproduction starts at any position in the magnetic tape, if all of one frame of a video signal is not recorded at the position, video cannot be displayed.
In the method for recording digital data which includes a video signal and an audio signal compressed by the MPEG-2 method, it is known that data especially for variable-speed reproduction, such as for searching, namely, search data, is recorded in each track of magnetic tape together with other types of data.
Depending on a position where search data is recorded on a track, however, the following problem arises.
An RF output obtained from each track differs between a normal reproduction mode (FWD) and a variable-speed reproduction mode, such as a high-speed reproduction mode (Cue and review) and a fast-forward or rewinding reproduction mode (FF and rewind) as shown in FIGS. 5 to 7. In FWD, a successful RF level is maintained at both starting position and ending position of a head in a track, whereas an RF output deteriorates at the start position of the head in a track where a rotating drum provides a thick air film in Cue and review (at about a speed five times to 30 times the normal reproduction speed). In FF and rewind (at about a speed 30 times to 200 times the normal reproduction speed), an RF output deteriorates near the ending position of a head in a track as well as the starting position in the track.
Therefore, in the DV method, for example, since position information (such as a track number) to be referenced during FF and rewind on the magnetic tape is recorded in the sub-code (Sub-code) sector, which is located near the ending position of a head in a track as shown in FIG. 4, it is difficult to obtain a necessary RF output.
When a non-standard signal (a signal output from a video-game unit or an analog-type recording and reproduction apparatus during a variable-speed reproduction, in which the time axis shifts from the standard of the NTSC system or the PAL system) is recorded by a digital-type recording and reproduction apparatus, if the rotation of a rotating drum tracks the non-standard signal, the length of each track into which digital data having a constant clock frequency is recorded may be extended or contracted.
As shown in FIG. 8, if the length of a track is extended, since the ending position of the head in the track shifts, data may be recorded into an area where an RF output characteristic is not assured on magnetic tape.
This issue is likely to affect especially methods in which a sub-code (Sub-code) sector is located near the ending position of a head in a track, such as the DV method. If data recorded into the sub-code (Sub-code) sector cannot be read, the destination is not identified in searching, causing a problem in the operations of the apparatus.
Accordingly, it is an object of the present invention to improve RF and search characteristics when data dedicated to variable-speed reproduction, such as a search, namely, search data, is recorded into magnetic tape, in a magnetic recording and reproduction apparatus and a method therefor in which compressed digital data is recorded into the magnetic tape by a helical scanning method or compressed digital data recorded into the magnetic tape by the helical scanning method is reproduced.
The foregoing object is achieved in one aspect of the present invention through the provision of a recording and reproduction method for recording compressed digital data on magnetic tape by a helical scanning method or for reproducing compressed digital data recorded on magnetic tape by the helical scanning method, including the steps of disposing sequentially in the direction from the top to the end of each track on the magnetic tape a first recording area, including an audio sector, and a second recording area, including a track-synchronization-information sector, a video sector or a video-and-audio-mixed sector in which audio data and video data are mixed, a sub-code sector, and a search-data sector in which data used in variable-speed reproduction is recorded, with an interference area disposed therebetween; recording data continuously in each sector in the first recording area and the second recording area; and disposing the sub-code sector or the search-data sector after the video sector or the video-and-audio-mixed sector in the second recording area.
Since the sub-code sector or the search-data sector is disposed at a position where a successful RF output characteristic is obtained in each track, the RF characteristic and that in the variable-speed reproduction are maintained at a successful level.
The foregoing object is achieved in another aspect of the present invention through the provision of recording and reproduction apparatus for recording compressed digital data on magnetic tape by a helical scanning method or for reproducing compressed digital data recorded on magnetic tape by the helical scanning method, including recording means for disposing sequentially in the direction from the top to the end of each track on the magnetic tape a first recording area, including an audio sector, and a second recording area, including a track-synchronization-information sector, a video sector or a video-and-audio-mixed sector in which audio data and video data are mixed, a sub-code sector, and a search-data sector in which data used in variable-speed reproduction is recorded, with an interference area disposed therebetween, and for recording data continuously in each sector in the first recording area and the second recording area, wherein the sub-code sector or the search-data sector is disposed after the video sector or the video-and-audio-mixed sector in the second recording area.
Since the sub-code sector or the search-data sector is disposed at a position where a successful RF output characteristic is obtained in each track, the RF characteristic and that in the variable-speed reproduction are maintained at a successful level.
The video sector or the video-and-audio-mixed sector, the sub-code sector, and the search-data sector may be disposed in that order in the second recording area in the direction from the top to the end of each track. In this case, data required for variable-speed reproduction is collectively disposed at the ending position (the last reading portion) of the head in a recording track, where a rotating drum provides a thin air film and a stable RF output is obtained. Therefore, the RF characteristic and that in the variable-speed reproduction are maintained at an extremely successful level.